The invention relates to Vertical External Cavity Surface Emitting Laser devices (VeCSEL) which allows achieving high coherence, power and tunability.
The field of the invention is, but not limited to, semiconductor laser sources for metrology and telecom applications.
Vertical External Cavity Surface Emitting Laser devices (VeCSEL) are well known devices.
They comprise basically a semiconductor element with a gain medium for generating the optical radiation and a first mirror.
The gain medium may comprise for instance quantum wells or quantum dots. It may be electrically or optically pumped.
The first mirror may comprise a succession of layers constituting a Bragg grating which reflects the optical waves around the laser frequency.
A second external mirror is provided and arranged so as to form an external optical cavity with the first mirror.
This kind of lasers has several advantages, such as a high intrinsic stability and a good tunability, which may be achieved by moving the external mirror for adjusting the length of the external cavity.
However, none of the known designs allows obtaining simultaneously high coherence, high power and large tunability.
High coherence and/or high frequency stability are usually achieved by introducing an etalon plate or an absorption cell into a long external cavity. In that case, the tunability is lost.
In order to obtain a broad tunability without mode hops, it is necessary to use a short external cavity with a large Free Spectral Range (FSR).
Finally, generating high powers leads usually to thermal dissipation problems in the semiconductor element and generation of thermal lenses (by modulation of the indices of refraction in the material) which induce a degradation of the laser performances in terms of spatial and temporal coherence.
There is a need for compact laser sources which combine high coherence, high power and large tunability, especially in the Mid-Infrared range (MIR) or in the Near Infrared Range (NIR), for applications such as sensing, spectroscopy . . . .
It is an object of the invention to provide laser sources which allow achieving high coherence, high power and broad tunability.
It is another object of the invention to provide laser sources which allow achieving high-power operation with good coherence and good stability.
It is another object of the invention to provide laser sources which allow achieving very high coherence and tunability over a broad frequency range.